feat: Add disabledPicker property to FormBuilderDateTimePicker

[CesareIsHere]

This PR adds support for the readOnly property to FormBuilderDateTimePicker, bringing it in line with other form builder fields and Flutter's native TextField behavior.

Changes Made

• Added readOnly property to FormBuilderDateTimePicker constructor with default value false
• Modified the onTap callback to conditionally prevent picker dialogs from opening when readOnly is true
• Updated documentation for the new property

Behavior

When readOnly: true:

• ✅ Field displays the current date/time value normally
• ✅ Date/time picker dialogs do not open when tapping the field
• ✅ Field maintains normal visual appearance (not grayed out like enabled: false)
• ✅ Field remains focusable for accessibility
• ✅ Value is still accessible for form submission and validation
• ✅ Consistent with other FormBuilder fields API

Usage Example

FormBuilderDateTimePicker(
  name: 'created_date',
  readOnly: true,
  initialValue: DateTime.now(),
  decoration: InputDecoration(
    labelText: 'Creation Date',
    hintText: 'This field is read-only',
  ),
)

Use Cases

• Displaying creation/modification timestamps
• Showing calculated dates that shouldn't be modified
• Form sections that are conditionally editable based on user permissions
• Confirmation/review screens where data should be visible but not modifiable

Breaking Changes

None - this is a backward-compatible addition with a sensible default value.

[deandreamatias]

Nice! Is useful new use for property but I think that could use decoration.readonly for this propouse.

[CesareIsHere]

@deandreamatias the problem with decoration.readOnly is that the field is always in readOnly because the value is insert through the date picker. The goal of this feat is to disable input using picker.

[deandreamatias]

@CesareIsHere so maybe need another name, to avoid confusion.
Something like disableOpenPicker or any else better

[CesareIsHere]

@deandreamatias That sounds good, thank you!
I renamed it to disablePicker

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 89.88%. Comparing base (84dbb3f) to head (a4a8574).
Report is 3 commits behind head on main.

Additional details and impacted files

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  Coverage   89.88%   89.88%           
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  Files          21       21           
  Lines         840      840           
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  Hits          755      755           
  Misses         85       85           

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